Polyphenylene ethers (PPE) are known to be endowed with excellent dielectric properties such as dielectric constant and loss tangent, and to have excellent dielectric properties even in the MHz to GHz high-frequency bands (high-frequency regions). Hence, polyphenylene ethers are being investigated for use as, for example, molding materials for high-frequency applications. Specifically, their suitability for use as, e.g., substrate materials for printed wiring boards to be provided in electronic equipment that utilizes high-frequency bands, is under investigation.
At the same time, when used as molding materials for substrate materials and the like, in addition to having excellent dielectric properties, polyphenylene ethers are also required to have excellent heat resistance, moldability and other properties. However, because polyphenylene ethers are thermoplastic, they have sometimes lacked the ability to achieve a sufficient heat resistance. It is thus conceivable, for example, to use a polyphenylene ether to which a thermoset resin such as an epoxy resin has been added, or to use a modified polyphenylene ether.
Accordingly, the applicant has proposed, as a modified polyphenylene ether-containing resin composition, the modified polyphenylene ether compound-containing resin composition described in Patent Literature 1.
Patent Literature 1 describes a polyphenylene ether resin composition which includes a polyphenylene ether having a polyphenylene ether moiety within the molecular structure, a p-ethenylbenzyl group or m-ethenylbenzyl group on a molecular end thereof and a number-average molecular weight of from 1,000 to 7,000, and which also includes a crosslinkable curing agent.
In the polyphenylene ether resin composition described in Patent Literature 1, the PPE is three-dimensionally crosslinked; even in cases where a low-molecular-weight PPE is used to increase the flowability of the PPE resin composition, the composition includes a crosslinking agent so as to retain properties such as heat resistance. Triallyl isocyanurate (also referred to below as “TAIC”) is used as this crosslinking agent.
However, the TAIC serving as this crosslinking agent has a reactivity contributing to the curing reaction which is somewhat low, and so a relatively large amount of reaction initiator must be added. This is because, when TAIC is included, with the addition of too little reaction initiator, the reaction slows and the glass transition point (Tg) does not easily rise. However, adding a bit too much reaction initiator may worsen the life of the varnish or prepreg obtained from the resin composition.
Moreover, with requirements for various properties in the insulating layers of recent printed wiring boards, etc. now more exacting than ever, there exists today a desire for substrate materials which, while retaining excellent dielectric (electrical) properties, are also endowed at even higher levels with such properties as heat resistance, adhesion and Tg.